Adolescence is a developmental period involving both heightened reward sensitivity and risk for bipolar spectrum disorders (BSDs). Despite their prevalence and public health significance, major unanswered questions exist regarding the mechanisms involved in vulnerability to BSDs. Recent exciting research provides strong and consistent support for a Behavioral Approach System (BAS)/reward hypersensitivity theory of BSDs that shows great promise for elucidating and integrating the neurobiological, behavioral, and environmental mechanisms underlying risk along the bipolar spectrum. In addition, research on social and circadian rhythm models of BSDs is also very promising, but has proceeded independently of research on reward sensitivity. Yet, our recent work demonstrates influences of reward sensitivity on social rhythm disruption and mood symptoms, leading us to a novel integration of reward sensitivity and social rhythm dysregulation in this application. Thus, the overarching goal of this proposal is to use an innovative biobehavioral high-risk design in adolescents to examine two interrelated processes that may help explain the association between reward hypersensitivity and BSDs: 1) heightened activation of a reward-related neural network involving the ventral striatum and orbitofrontal cortex; and 2) influences of reward sensitivity/activation on social rhythm disruption. We will continue to follow High and Moderate BAS/reward sensitive adolescents as they further age into the period of risk for BSDs with self-report and behavioral measures of reward sensitivity/processing, BAS-relevant cognitive styles, social rhythms, BAS-relevant and social rhythm disruption life events, and mood symptoms/ diagnoses. We also will conduct a new and novel neuroimaging study. We will compare High BAS adolescents who have developed BSD (HBAS+BSD), High BAS adolescents who have not yet exhibited, but are at risk for, BSD (HBAS), and Moderate BAS adolescents without BSD (MBAS) on reward-related brain activity and connectivity in response to the anticipation and receipt of monetary rewards in an fMRI study. In addition, we will examine the influence of reward sensitivity/activation and social rhythm dysregulation on mood symptoms in these same three groups of adolescents. This research program is the first to examine neural trait markers and social rhythm dysregulation in adolescents at risk for BSDs based on a hypothesized psychobiological vulnerability. It will provide tools for the early identification of adolescents at risk for first onset and a worse course of BSD, inform our understanding of specific etiological pathways and biobehavioral mechanisms involved in illness onset, recurrence, and progression, and contribute to the development of early psychosocial, pharmacological, and neuroprotective strategies targeted at ameliorating reward processing abnormalities.